You can cure that condition by installing the VCOSHLDMD from Elecraft.
It adds a mu-metal shield around T5 so the transformer core is not
modulated by the magnetic field from the power supply transformer.
If you do install that mod, first adjust the T5 turns spacing and then
put the shield around T5 and make a final adjustment by moving the end
turns of the red winding a bit closer together or further apart.
That last step is not mentioned in the instructions, but I have found it
necessary.
73,
Don W3FPR
On 10/31/2020 12:06 PM, Louandzip via Elecraft wrote:
I got bad TX hum when I temporarily place my K2 on top of a 35A Astron power
supply. Seemed to be from the transformer's leaked magnetic field and went
away if I lifted the K2 just an inch or two. I'm sure I posted about it in
the reflector, but that was pushing 20 years ago. My call might have been
different at the time.
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